Refraction
is evidence of the wave nature of light - we can only explain refraction
in terms of waves.

Wavespeed changes when a wave moves from one medium to another. (See here for more detail). That makes the wave refract.

Refraction of light

If a light ray speeds up it bends away from the normal - i.e. it makes a bigger
angle with the normal than it did before - it swivels away from the normal.

... and if a ray slows
down it bends towards the normal - i.e. it makes a smaller angle with
the normal than it did before - it swivels towards the normal.

Refraction of sound

When
you are dealing with 'sound' waves remember that sound waves travel fastest
in dense media and slower in less dense ones. Therefore for sound waves
refraction towards the normal indicates a speeding up of the wave! - see
seismic
waves